This specification relates to wavelength division multiplexing.
Conventional wavelength division multiplexing (“WDM”) allows a single optical fiber to transmit a signal having multiple light streams where each light stream can have a different wavelength. Carrying multiple light streams of different wavelengths increases the bandwidth of the signal where the total bandwidth is the sum of the bandwidth provided by each individual wavelength.
Typically, to combine multiple light streams (e.g., eight individual light streams with wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8, respectively), individual light streams are incrementally combined to form a single signal including the wavelengths of all (e.g., eight) individual light streams. For example, light streams with wavelengths λ1 and λ2, respectively, are combined to form a single light signal including the two wavelengths, λ1 and λ2. Similarly, the light signal having wavelengths λ1 and λ2 is again combined with the third light stream including wavelength λ3 to form a single light signal including three wavelengths λ1, λ2, and λ3. This process of adding light streams is repeated until a single light signal including eight wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 is formed. The resulting light stream having multiple wavelengths is typically referred to as a wavelength division multiplexed signal.
Additionally, a wavelength division multiplexed signal can also be decomposed to form one or more light streams, each including one or more wavelengths. Decomposing a multiplexed signal is typically referred to as demultiplexing. Conventional demultiplexing is the reverse process of multiplexing. The multiplexed signal, which, for example, is a single light stream including eight wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8, is directed to a filter. The filter transmits light having a single wavelength, for example λ1, and reflects light, including wavelengths other than λ1. Consequently, when the multiplexed light stream including wavelengths λ1, λ2, λ3, λ4, λ5, λ6, λ7, and λ8 is incident onto a filter of λ1, the filter passes a light stream including wavelength λ1, and reflects a second multiplexed light stream, which includes only seven wavelengths: λ2, λ3, λ4, λ5, λ6, λ7, and λ8.
A conventional demultiplexing device typically has three ports. The multiplexed signal including multiple wavelengths is input into the first port. The second port outputs the light stream passed by the filter (e.g., having only one wavelength λ1), and the third port outputs the light stream reflected from the filter (e.g., having seven wavelengths λ2, λ3, λ4, λ5, λ6, λ7, and λ8). Multiple filters arrangements can be used to separate out streams having other wavelengths.